Download Mesoscale convective complex genesis and forecast in Alagoas

Journal of the Georgian Geophysical Society,
Issue B. Physics of Atmosphere, Ocean and Space Plasma, v. 12B, 2008, pp. 36-44.
Mesoscale convective complex genesis and forecast
in Alagoas State of Brazil
Natalia N. Fedorova, Vladimir I. Levit, Luiz R. L. Rodrigues, Saulo B. Costa
Institute of Atmospheric Science, Federal University of Alagoas, Brazil
Cumpus A.C.Simoes, BR-104 Norte km 96,7, Tabuleiro dos Martins, Municipio de
Maceio, Estado de Alagoas, Brazil, [email protected]
Abstract
Significant precipitation, thunderstorm, floods and other extreme weather events, which have caused
problems in Alagoas State, were investigated. NCEP reanalysis data, HYSPLIT model trajectories,
satellite images and adjacent Atlantic Ocean thermal conditions were used for the investigation. Wave
Disturbance in the field of Trade Winds (WDTW) on the northwest periphery of subtropical High were
associated with a different processes of clouds formation, which are possible to create both Cb and Stclouds. Periphery of the frontal zones rest were one of the causes of the WDTW formation far from other
synoptic systems. The WDTW were associated with Mesoscale Convective Complex (MCC). Very height
air instability (CAPE=3936J/Kg and LI=-7) was typical for these events. Extreme events forecast were
elaborated by instability indexes and a convective available potential energy (CAPE) calculated by
forecasted vertical profiles using. These profiles were constructed by Air Parcels Trajectories of
HYSPLIT model. The ocean surface heating near Alagoas and baric trough at low levels were associated
with the thunderstorm development in some MCC events. In other MCC a very weak jet stream at high
levels near Alagoas was identified as a principal process for ascendant motion formation. The 12h-24h
antecedent forecasted vertical profiles were helped for extreme events forecast.
1. Introduction
Some meteorological adverse phenomena, such as, significant precipitations, thunderstorms,
stratus clouds, floods, etc, have caused a lot of problems in Alagoas State (North- East coast of Brazil,
10oS approximately). Theses phenomena were associated with low level trough Gomes and Fedorova;
Levit et. al.; Fedorova, et al. [1-5]. These troughs geneses did not well known yet.
The wave can reflect a Intertopical convergence zone (ITCZ), or a cold Low in the upper
troposphere (known also as Upper Troposphere Cyclonic Vortex - UTCV), or may by associated with
equator extension of mid-latitude baroclínic trough. Also, a wave was defined by Simpson [6] as a trough,
or cyclonic curvature maximum, in the trade wind. The barotropic wave may reach maximum amplitude
in the low or middle troposphere.
The first kind of wave, which was described in the Tropics, was Easterlies Waves in the
Caribbean area (Barry and Chorley [7] ). There are some weak barotropic troughs in the tropical regions.
These troughs axis are usually inclined eastward with height. Frequently, Cumulonimbus clouds develop
and thunderstorm occur in these weak troughs behind their axis passage. This pattern is associated with
vertical and horizontal motion in the easterlies. An air convergence has occurred behind of the low-level
weak trough axis and a divergence have detected in front of it.
One of the wave study problems is the detection difficulty of exact beginning of the wave
formation. This is especially true in the tropic regions because of restrict meteorological data, insufficient
knowledge of a synoptic systems development and absence of the numerical meteorological models
suitable for this region (Riehl; Tenorio et al. [8,9] ). It is sure that many waves in the Atlantic Ocean are
formed over the African coast or near. Another factor, which can initiate waves in the easterlies, is a
penetration of cold fronts into low latitudes (Riehl; Barry and Chorley; Tenorio et al.; Molion and
Bernardo [7 - 10]). This is a common phenomenon in the section between two subtropical anticyclones.
This work aim is an investigation of intensive convection development in troughs near the
Alagoas State to support the short-term weather forecast.
36
2. Method
The conventional data were used for adverse phenomenon identification. The identification of
Mesoscale Convective Complex (MCC) was made according to description of Veltishev [11]. The vertical
profiles were constructed by NCEP reanalysis data for Maceio city. The radiosonde data were used to
complement the NCEP profiles. The synoptic situation before and during adverse events were analyzed
using satellite images and different products of NCEP reanalysis: streamlines (at the levels of 1000, 925,
500 and 200hPa), surface pressure, omega, temperature and relative humidity at the 925, 850, and
1000hPa levels, thermal advection at the low levels. The software “Grads” (Doty [12]) was used to
elaborate all maps.
Air Parcels Trajectories of HYSPLIT model was used to calculate forecasted trajectories for
Maceio city (Alagoas State), with 12-48 h antecedence. These trajectories were used to construct of the
forecasted vertical temperature and humidity profiles. The strong convection forecast was made using K,
TT, LI indexes and positive CAPE (Convictive Available Potential Energy), calculated by forecasted
vertical profiles.
3. Results
Three extremely adverse meteorological events with different formation processes are presented
below. Significant precipitations, thunderstorms and floods were associated with these MCCs
development.
The first MCC was observed 12 June 2002. An infrared satellite image (Figure 1a) shows a
convective cloud system (MCC) near Northeastern of Brazil (NEB). The trough at the low levels, which
is a wave disturbance in the field of trade winds (WDTW), near Alagoas State, was an important reason
for the MCC devolvement (Figure 1b). The trough motion to westward at 500hPa level is presented at the
Figure 2. This trough axis was over Alagoas State on 11 June, 00 UTC; its rearguard was over Alagoas
State on 12 June, 00 UTC, on the MCC developed day. Therefore, a weak trough at the low and middle
levels was considered as the first cause for very strong convection and consequently MCC development.
(b)
(a)
Figure 1 – (a) METEOSAT Satellite IR image and (b) streamline at 1000hPa level for 12 June
2002 at 12UTC. Source: CPTEC/INPE, NCEP.
10/06 00UTC
10/06 12UTC
11/06 00UTC
11/06 12UTC
12/06 00UTC
Figure 2 – Streamline at 500hPa level for 10-12 June 2002. Source: NCEP
37
12/06 12UTC
The trajectories show the connection between the MCC development and the trade winds at the
low levels and the trough at the middle levels (Figures 2 and 3). Also, some warm thermal wave at low
levels and cold thermal wave at the middle levels were detected by the trajectories analyses (Figures 3
and 4).
(a)
(b)
(c)
(d)
Figure 3 - Air Parcels Trajectories of HYSPLIT model in vertical and horizontal outline at about 1500,
3000, 5000 e 9000m.
The Air Parcels Trajectory with 12 antecedence superimposed on temperature field show an
influence of positive thermal advection from the warm wave at 850hPa level, from the warm center at
700hPa level and negative advection at 500hPa (Figure 4a, b and c, respectively). This thermal advection
vertical distribution creates the perfect conditions for the instability development and the MCC formation.
In this MCC case, the sea surface temperature was cold and did not influence to the latent heat liberation
(Figure 4d).
The forecasted vertical profiles for the Maceio City are presented (Figure 5). The K (K=29 and
26, to 12 and 24hr forecasted profiles, respectively) and LI (LI= -4,5 and -3,5, to 12 and 24hr forecasted
profiles, respectively) indexes were used to showers forecast with 12 and 24h antecedence (indexes
interpretation by Djuric [13]). The positive CAPE values permitted to predict the strong convection with
12h antecedence.
(a)
(c)
(b)
(d)
Figure 4 – Air Parcels Trajectory with 12h antecedence inside temperature field for 12 June 2002 at
00UTC at the levels: 850(a), 700(b) and 500hPa(c); (d) weekly sea surface temperature anomaly
between June 10 and 16 2002. Source: NCEP; ECMWF
(a)
(b)
(c)
(d)
Figure 5 - Forecasted vertical profiles calculated by Air Parcels Trajectories of HYSPLIT model with
12h (a), 24h (b), 36 (c) and 48h (h) antecedence.
38
The second MCC was developed on 15 June 2003. Satellite images show the MCC near the
Alagoas State and jet steam cloudiness (Figure 6). This very weak jet steam (with wind velocity near
30ms-1) was confirmed by streamlines at 200hPa level (Figure 7b). This atypical weak jet steam near
NEB had already identified before by Gomes [14] near the UTCV. In this present case this jet stream
causes a very strong ascendant motions and MCC formation (Figure 6b). The WDTW near NEB at the
low levels (Figure 7a) and direct ageostrophic circulation around the jet stream contributed to ascendant
motion development.
(a)
(b)
Figure 6 - METEOSAT Satellite IR image for 15 June 2003: (a) 00 and (b) 12UTC. Source:
CPTEC/INPE
(a)
(b)
Figure 7 - Streamline for 15 June 2003 at 00UTC: (a) 1000 and (b) 200hPa.
Source: NCEP
The Air Parcels Trajectories (Figure 8) were used to elaborate the forecasted vertical profiles
(Figure 9). By the using of the K, TT, LI indexes and positive CAPE values it was not possible to forecast
the intensive convection development: the positive CAPE were less than 1000 J/Kg and LI index was
more than -2 for 12-48h antecedence. Therefore, the strong convection could not be forecasted by theses
vertical profiles.
(a)
(b)
(c)
(d)
Figure 8 - Air Parcels Trajectories of HYSPLIT model in vertical and horizontal outline at about 1500,
3000, 5000 e 10000m.
39
Figure 9 - Forecasted vertical profiles calculated by Air Parcels Trajectories of HYSPLIT model with
12h (a), 24h (b), 36 (c) and 48h (h) antecedence.
At the same time, the jet stream and intensive vertical ascendant motions were registered by
vertical sections (Figure 10a, b, and c). This jet stream was shallow, localized at high levels up to 400hPa
and formed by a very deep and strong latitude jet stream component. The jet stream and low levels trough
near NEB have formed two circulations: one at the high and another at low levels, respectively (Figure
10b). Both circulations have created an ascendant motion column close to Alagoas State and sequentially
were responsible for the MCC formation on 15 June 2003.
(a)
(b)
(c)
(d)
Figure 10 – Vertical sections along 36oW: (a) u component wind vertical section, (b) divergence
vertical section, (c) omega vertical section for 15 June 2003 at 00UTC. Weekly sea surface temperature
anomaly between June 8 and 15 2003 (d). Source: NCEP; ECMWF
The third MCC was observed 4-5 March 2002. Extremely intensive precipitations, above average
values, have been registered from 4 to 5 March 2002 in the State of Alagoas and were associated with
MCC development. The precipitations of more than 100mm/24h were observed by four meteorological
stations, more than 70mm/24h by 11 stations and more than 50mm/24h by 19 stations on 4 March. The
highest precipitations of 130 mm/24h and average precipitations of 42,8 mm/24h were detected on the
same day. The maximal precipitation intensity was 6.2 mm/1h on 4 March, 16h and 8.6mm/1h on 5
March, 1h (local time). The conventional meteorological 10 min observations show that the maximal
precipitation intensity on 5 March was registered at 16h (local time) immediately after maximal solar
radiation increase and relative humidity decrease.
Table 1 – Average and maximal (max) precipitation (mm/24h) in the ambient regions of Alagoas State on
3, 4 and 5 March 2002.
Region
precipitations
Day 3
Day 4
Day 5
average
max
average
max
average
max
Litoral
2,08
13,0
66,71
123,0
12,5
36,0
Zona da Mata
6,27
22,8
60,2
130,0
8,83
27,0
Sertão
0,24
1,2
27,0
48,0
5,4
27,0
Sertão do São Francisco
0,05
0,2
5,8
23,0
27,2
56,4
Agreste
1,1
2,2
49,9
95,8
34,0
68,0
2,65
5,2
46,95
93,6
5,17
12,6
Baixo São Francisco
Average in the State
2,07
7,43
42,80
85,57
15,50
37,83
40
The MCC development was associated with WDTW, which was formed between both
hemispheres trade winds near the Intertropical Convergence zone (ITCZ) (Figure 11a). The WDTW was
observed only at the low levels (up to 850hPa) and above the anticyclonic air current was predominated
(Figure 11b). The divergence current in ITCZ near equator and air convergence to south from Alagoas
State at the high levels were accompanied by the MCC development. These synoptic scale currents have
created the convergent air current at the low levels and the divergent current at the high levels and as a
consequence have created favourable conditions of ascendant motions and MCC formation.
.
(b) 500hPa
(a) 1000hPa
Figure 11 - Streamlines for 4 March 2002 at 12UTC at the levels 1000 (a) and 200hPa (b).
Source: NCEP
The intensive convection development was observed in cloudiness by infrared satellite images
above the whole Alagoas State (Figure 12). Also, theses images show that this convection is associated
with the south part of the ITCZ cloudiness.
(a) 4 March, 00 UTC
(b) 4 March, 19:30 UTC
(d) 5 March, 20:30 UTC
Figure 12 - GOES Satellite IR image for 4 and 5 March 2002. Source: CPTEC/INPE
The intensive instability was calculated by vertical profiles, constructed by NCEP reanalysis for
Maceio city, and by radiozond data in Natal (Table 2, Figure 13). The highest values were obtained for
intensive precipitation time in Maceio and reached LI = -3 e CAPE = 1139J/Kg. The convection in Natal
was more intensive and instability parameters by radiozond have reached extremely high values (CAPE =
3936J/Kg e LI = -7). It is important to note, that calculated instability parameters by NCEP reanalysis
were 3 times less than calculated by radiozond data. The highest vertical temperature gradient at the low
level up to 970hPa and high humidity at all troposphere levels up to 350hPa were responsible for
extremely intensive convection development. The precipitation stopping was associated with superficial
instability decreasing.
41
Table 2 – Instability parameters (indexes K, TT, LI and CAPE, J/Kg) by NCEP reanalysis for days 3, 4 e
5 March 2002 in Maceio city and by radiozond in Natal. Source: NCEP, CPTEC/INPE.
Day / hour / city
03/ 00UTC / Maceio
03/ 12UTC / Maceio
04/ 00UTC / Maceio
04/ 12UTC / Maceio
05/ 00UTC / Maceio
05/ 12UTC / Maceio
03/ 12UTC / Natal
04/ 12UTC / Natal
K
27
27
30
25
34
32
29
25
TT
40
41
43
40
44
43
45
44
(b)
LI
-1
-2
-2
-1
-3
-3
-7
-7
CAPE
344
847
542
990
1139
1078
3380
3936
(c)
Figure 13 - Vertical profile calculated by NCEP reanalysis data for Maceio city, 4 March, 12UTC (a)
and vertical profile by radiosonde in Natal, 4 March, 12UTC (b). Source: NCEP, CPTEC/INPE
The wind direction variation with height increase, obtained by radiozond and NCEP reanalysis
profiles, promoted the convection intensification. All these data show the wind direction variation to
left at low levels and to right at the high levels (Figure 13). Theses wind variations are associated with
warm advection at the low levels and with cold advection at the high levels. Consequently, this
thermal advection height distribution has increase instability and convection.
The principal results of this investigation show that difficulties of such events forecast are the
result of restrict meteorological data, insufficient knowledge of a synoptic systems development and
absence of verification of the numerical meteorological models suitability over this region. The
WDTWs on the north-western periphery of subtropical High were associated with all events of MCC
development. Peripheries of the frontal zones rest were one of the causes of WDTW formation which
were localised far from other synoptic systems. The weak jet stream near NEB have created the direct
ageostrofic circulation, which intensified vertical motions and MCC formation in other case. At the
third case, the vertical distribution of thermal advection (warm advection at the low levels and cold
advection at the high levels) have increased increases instability for extremely intensive MCC
development.
Very high air instability (up to CAPE=3936J/Kg and LI=-7) was typical for two MCC events
and in one MCC the high instability (CAPE ≤1000 J/Kg and LI ≥-2) didn’t identified. The instability
parameters, calculated by NCEP reanalysis profiles, were less than calculated by radiozond data. The
ocean surface heating near Alagoas State and thermal air advection at the low levels were associated
with the thunderstorm development only in some MCC events. In other MCC a very weak jet stream
at high levels near Alagoas area was identified as a principal process for ascendant motion formation.
The vertical profiles, elaborated by Air Parcels Trajectories of HYSPLIT model, were useful to
forecast one extreme event with 12h-24h antecedent.
42
References
[1] H. B. Gomes, N. Fedorova - Analise dos produtos do modelo ETA de alta resolução para o
Estado de Alagoas parte III: Nuvens Stratus associadas aos ventos alísios. In: XIII Congresso
Brasileiro de Meteorologia, Fortaleza, Anais... 2004 , (CD-ROM).
[2] N. Fedorova, S. O. Krichak, V. Levit, M. H. Carvalho, , L.R.L. Rodrigues - Verificação das
trajetórias das parcelas de ar pelo modelo HYSPLIT no caso de CCM em Maceió-Alagoas. In: XIII
Congresso Brasileiro de Meteorologia, Fortaleza, Anais... 2004, (CD-ROM).
[3] N. Fedorova, V. Levit, L. R. L. Rodrigues, A. R. Fonseca - Corrente de jato no NEB e múltiplos
fenômenos meteorológicos adversos no Estado de Alagoas, Brasil, no dia 15 de junho de 2003. In: IX
Congreso Argentino de Metereología, Buenos Aires, Anais..., 2005 ,(CD-ROM).
[4] V. Levit, N. Fedorova, G. C., Pereira - Analise dos produtos do modelo ETA de alta resolução
para o Estado de Alagoas. Parte VII: Intensa trovoada em Maceió no dia 18 de janeiro de 2004. In:
XIII Congresso Brasileiro de Meteorologia, Fortaleza, Anais..., 2004 ,(CD-ROM).
[5] V. Levit, N. Fedorova, S. B. Costa, H. B. Gomes, G. C. Pereira, R. M. C. P. Miranda, Fenômenos adversos associados às perturbações ondulatórias nos ventos alísios no Estado de Alagoas
- Brasil. In: IX Congreso Argentino de Metereología, Buenos Aires, Anais., 2005 ,(CD-ROM).
[6] R. H. Simpson, N. Frank, D. Shideler, H. M. Johnson - Atlantic Tropical Disturbances, Monthly
Weather Review, Vol. 96, No. 4, 1968, pp.251-259.
[7] R. G. Barry, R. J. Chorley - Atmosphere, weather and Climate, 4th edition. Methuen, New York,
1982, 407 p.
[8] H. Riehl - Tropical Meteorology. McGraw-Hill, New York, 1954, 392p.
[9] R. S. Tenorio, L. C. B. Molion, H. Sauvageot, D. de Assis Quintao, A. M. de Agostinho Radar rainfall studies over Eastern Coast of Northeast Brazil. In: 31th Radar Meteorology Conference,
Seattle, USA, 2003.
[10] L. C. B. Molion, S. O. Bernardo - Uma Revisão da Dinâmica das Chuvas no Nordeste
Brasileiro. Revista Brasileira de Meteorologia, v.17, n.1, 2002, pp. 1-10.
[11] N.F. Veltishev - Mesometeorology and short – range forecasting. Lecture notes and student’s
workbook for training Class I and Class II Meteorological personnel. WMO., 1990, 163 p.
[12] B. Doty - The Grid analysis and display system. Version 1.8SL11, 2001,
http://grads.igds.org/grads/.
[13] D. Djuric - Weather Analysis. New Jersey: Prentice Hall, 1994, 304p.
[14] H. B. Gomes - Estudo da corrente de jato próximo ao Estado de Alagoas. MSc. Thesis, Federal
University of Alagoas, Maceio, Brazil, 2003, 113p.
(Received in final form 23 November 2008)
Генезис и прогноз мезомасштабного конвективного
комплекса в штате Алагоас, Бразилия
Наталья Н. Федорова, Владимир И. Левит, Луиз Р.Л. Родригес, Сауло
Б. Коста
Резюме
Проведено изучение обильных осадков, гроз, наводнений и других экстремальных
явлений погоды, которые вызвали проблемы в штате Алагоас. При исследованиях были
использованы данные NCEP, модель траектории воздушных частиц HYSPLIT, спутниковые
изображения и граничные температурные значения Атлантического океана. Волновые
43
возмущения в области пассата (WDTW) в северо-западной периферии субтропического
антициклона связаны с различными процессами формирования облаков, и возможно, Cb и St.
Периферийная область фронтальной зоны покоя была одной из причин формирования WDTW,
далекой от других синоптических систем. WDTW были связаны с Мезомасштабным
Конвективным Комплексом (MCC). Высокая неустойчивость воздушных масс (свободная
потенциальная энергия конвекции CAPE=3936Дж/ кг и индекс LI = -7) была типична для этих
событий. Прогноз экстремальных событий был разработан с использованием индексов
неустойчивости и данными о CAPE, вычисленными по прогностическим значениям их
вертикальных профилей. Эти профили были построены с использованием модели HYSPLIT.
Нагрев поверхности океана вблизи Алагоаса и барическая ложбина связаны с развитием гроз
при некоторых случаях MCC. В других случаях MCC очень слабое струйное течение на
больших высотах рядом с Алагоас было идентифицировано как основной процесс для
формирования восходящего движения.
12- и 24-часовые прогнозы указанных вертикальных профилей использовались для
прогнозирования экстремальных метеорологическия явлений.
მეზომასშტაბური კონვექტური კომპლექსის
გენეზისი და პროგნოზი ალაგოასის შტატში, ბრაზილია
ნატალია ნ. ფიოდოროვა, ვლადიმერ ი. ლევიტი, ლუიზ რ.ლ.
როდრიგესი, საულო ბ. კოსტა
რეზიუმე
ჩატარებულია უხვი ნალექების, ელჭექის, წყალდიდობების და ბუნების იმ სხვა
ექსტრემალური მოვლენების შესწავლა, რომლებმაც პრობლემები გამოიწვია ალაგოასის
შტატში. გამოკვლევებისას გამოყენებულ იქნა NCEP მონაცემები, ჰაერის ნაწილაკების
ტრაექტორიის HYSPLIT მოდელი, თანამგზავრული გამოსახულებები და ატლანტის
ოკეანის სასაზღვრო ტემპერატურული მნიშვნელობები. ტალღოვანი შეშფოთებები
სუბტროპიკული ანტიციკლონის ჩრდილო - დასავლეთის პასატის (WDTW) არეში
დაკავშირებულია ღრუბლების ფორმირების პროცესებთან და შეიძლება Cb და St.
სიმშვიდის ფრონტული ზონის პერიფერიული არე ერთ - ერთი მიზეზი იყო WDTW - ს
ფორმირებისა, რომელიც შორსაა სხვა სინოპტიკური სისტემებიდან. WDTW
დაკავშირებული იყვნენ მეზომასშტაბურ კონვექტურ კომპლექსთან. (MCC). ჰაერის
მასების მაღალი არამდგრადობა (თავისუფალი ენერგია კონვექციისა СAPE = 393 ჯ/კგ და
ინდექსი LI = -7) ტიპური იყო ამ მოვლენებისათვის. ექსტრემალური შემთხვევების
პროგნოზი შემუშავებული იყო არამდგრადობის ინდექსებისა და CAPE - ს მონაცემების
გამოყენებით,
რომლებიც
გამოთვლილია
მათი
ვერტიკალური
პროფილების
პროგნოსტული მნიშვნელობებით. ეს პროფილები შედგენილია HYSPLIT მოდელის
გამოყენებით. ალაგოასის მახლობლად ოკეანის ზედაპირის გათბობა და ბარიული
ღრმული დაკავშირებულია ელჭექების განვითარებასთან MCC - ის ზოგიერთ
შემთხვევაში. MCC - ის სხვა შემთხვევებში ალაგოასის მახლობლად ძალიან სუსტი
ნაკადური დინება დიდ სიმაღლეებზე იდენტიფიცირებული იყო, როგორც ძირითადი
პროცესი აღმავალი დინების ფორმირებისთვის.
12 და 24 საათიანი პროგნოზები აღნიშნული ვერტიკალური პროფილებისა
გამოყენებულ
იქნა
ექსტრემალური
მეტეოროლოგიური
მოვლენების
პროგნოზირებისათვის.
44